The synthesis of superconducting Tl–Ca–Ba–Cu–oxide films by the reaction of spray deposited Ca–Ba–Cu–oxide precursors with Tl₂O vapor in a two-zone reactor

Abstract

Superconducting Tl-Ca-Ba-Cu-oxide films have been prepared on yttria stabilized zirconia substrates via the reaction of T1 2 O vapor with precursor Ca-Ba-Cu-oxide films prepared by the spray pyrolysis of a solution of the metal nitrates. The vapor reaction process, evaluated in both air and oxygen ambients, was carried out in a two-zone reactor which permitted the independent control of the temperatures of the sample and of a boat containing thallium oxide. Sample temperatures of 865-905 °C and boat temperatures of 775-870 °C were investigated. X-ray diffraction analysis of the best samples, which were prepared in an oxygen ambient at sample temperatures of 895-900 °C and boat temperatures of 805-810 °C, revealed the presence of a highly oriented Tl 2 Ca2Ba 2 Cu3O 10+) , phase with a trace of the Tl 2 CaBa 2 Cu 2 0 8+r phase. FWHM's of ~ 2° 9 were obtained in x-ray rocking curve analyses of the oriented 2223 phase. T c (0) values of 95-105 K were measured for the better samples, and a zero field critical current density of 28 800 amps/cm 2 was measured at 77 K for the best sample. SEM micrographs taken of the highest J c samples reveal a highly textured structure consisting of platelike crystals.

Process optimization for the fabrication of Tl2Ba2Ca2Cu3O10 thin films

“…Both BaCaCuO and TlBaCaCuO precursor films have been used, and a variety of methods have been used in their preparation, including sputtering, 19-28 laser ablation, 29,30 evaporation, [31][32][33] and spray pyrolysis. 23,36 Other thallination techniques have also been attempted. 19,20,29,31,[33][34][35] A few studies have used a thallium oxide source held at a lower temperature than that of the film to maintain a thallous oxide overpressure.…”

Fabrication, Structure and Properties of Tl-Based HTS Thin Films

“…In this way the temperature of the film, and the partial pressures of ThO and O2 can be independently varied, resulting in greater control of the thalliation process. TI is transported to the film by molecular diffusion [14] or by a stream of flowing gas [15,16] as shown in Figure 3.. It might be supposed that this latter process, with its facility for independent control of all variables, will be the one to be developed for the production, on a commercial scale, oflarge area double-sided device quality films with reproducible properties.…”

Effect of annealing temperature on the structural-microstructural and electrical characteristics of thallium bearing HTSC films prepared by chemical spray pyrolysis technique

“…Because of their high T c (~ 125 K) and high J c , they are readily amenable to operation at liquid nitrogen temperature (~ 77 K). Uptil now, various methods for the preparation of HTSC thin films such as electron beam evaporation (Ramesh et al 1990;Ginley et al 1998a,b;Sugise et al 1998), sputtering (Lengfellner et al 1989;Lin and Wu 1989;Subramanyam et al 1990;Saito et al 1991;Ichikawa et al 1998;Zhou et al 1998), laser ablation (Betz et al 1989;Johs et al 1989), thermal flash evaporation (Barboux et al 1988;Ece and Vook 1989;Verma et al 1989), chemical spray pyrolysis (Kawai et al 1987;Gupta et al 1988;Saxena et al 1988;DeLuca et al 1991;Verma et al 1992) and spin coating (Rice et al 1987) etc have been employed. Out of these techniques, the simple chemical process like spray pyrolysis and spin coating are economically viable.…”